There is an ever increasing demand for power conversion and regulation circuitry to operate with increased efficiency and reduced power to accommodate the continuous reduction in size of electronic portable devices. Many times these devices are battery powered, and it is desirable to utilize as little power as possible to operate these devices so that the battery life is extended. Voltage regulators have been implemented as an efficient mechanism for providing a regulated output in power supplies. One such type of regulator is known as a switching regulator or switching power supply, which controls the flow of power to a load by controlling the on and off duty-cycle of one or more high-side switches coupled to the load. Many different classes of switching power supplies exist today.
One type of switching power supply is known as a buck synchronous switching power supply or step-down synchronous switching power supply. In a buck synchronous switching supply, an inductor is used to maintain current flow that is switched from two separate sources. The two sources can include a high-side switch, such as a high-side field-effect transistor (FET), and a low-side switch, such as a low-side FET. Upon the high-side FET being turned on, the inductor is coupled to a power source through the high-side FET, causing current to flow through the inductor and thus generating an output voltage. Once the high-side FET is turned off, magnetic energy stored in the inductor dissipates to force current through the inductor. In this way, current continuously flows through the inductor in the times between activation of the high-side and the low-side switches.
The duty-cycle at which a high-side switch activates may depend on an amount of load at the output of the switching power supply. As an example, a heavier output load draws more current, thus necessitating a greater duty-cycle of activation of the high-side switch to maintain a steady output voltage based on a steady current flow through the inductor. In certain implementations, the duty-cycle at which the high-side switch activates can vary commensurate with changes in the output load.
Upon a transition of the output load, for example, from a heavy load to substantially no load, the switching power supply may experience an output voltage overshoot condition. As an example, the duty-cycle of the high-side activation could be very high during the heavy load condition, such that, upon the load changing from a heavy load to substantially no load, the output voltage rapidly increases. Because there is substantially no load, substantially no current is drawn through the inductor. As a result, the switching power supply may be unable to discharge an output capacitor to settle the output voltage to the appropriate voltage potential within an amount of time required by specification.